Cladding material

ABSTRACT

Clad material comprises a metal substrate which is provided with a multiplicity of perforated openings therein and a metal foil which is laminated on the metal substrate to close the perforated openings. To produce such a clad material, at least one surface of the metal substrate and corresponding one surface of the metal foil are respectively subjected to a dry etching and the metal substrate and the metal foil are laminated in such a manner that the etched surfaces face each other. Alternately, only one surface of the metal substrate is subjected to a dry etching and the metal substrate and the metal foil are laminated in such a manner that the etched surface of the metal substrate defines a laminating surface. It may be possible to provide a nickel plating on the metal substrate or the metal foil. The clad material can be effectively used for producing safety valve chips which rupture accurately at low pressures which fall in a stable pressure range on a mass production basis.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to a clad material comprising a metalsubstrate having a multiplicity of perforated openings laminated with ametal foil.

2. Description of Related Art

Conventionally, batteries which use alkaline metal such as lithium,sodium or potassium as an active material on negative electrode thereofsometimes suffer from rupture when the pressure in the batteries isabnormally elevated. To prevent the occurrence of such a rupture, safetyvalves which can release the pressure outside in the case that thepressure in the battery is excessively increased have been requested andaccordingly various safety valves having different mechanisms have beenproposed. To assure the safety that even when the battery ruptures by achance, broken pieces or contents of the battery do not scatter outsideand cause no damage on human body, the batteries must be operated at alow pressure not more than 30 kgf/cm².

The dry-cell type battery which uses alkaline metal as the activematerial on negative electrode thereof is further required to have ahigh scalability. A Japanese laid-open publication SHO 63-285859discloses a safety valve which can release the inner pressure of such abattery outside. In this battery, a part of the wall of the batteryvessel is made thin by cold compressing using a press until thethickness of the compressed part becomes half of the original thicknessof the part. Accordingly, when the inner pressure is elevated andreaches a predetermined inner pressure level, the thinned wall partruptures and the inner pressure is released outside.

To release the inner pressure at a low pressure of not more than 30kgf/cm², the thinned wall part must be made considerably thin.Accordingly, during the press working to obtain such an extremely thinwall part, fine or minute cracks may occur, and once such cracks occur,the sealability of the vessel is spoiled. Although the thinned wall partis hardened with such a press working, the hardening does not occuruniformly. Accordingly, the release valve disclosed in Japaneselaid-open publication SHO 63-285859 also suffers from a drawback thateven when the thinned wall part is pressed to have a uniform thickness,the thinned wall part does not always rupture at a predetermined uniformpressure.

Furthermore, although an etching method has been proposed to make a partof the wall of the battery vessel thin, it is extremely difficult touniformly control the thickness of the thinned wall part after etchingand the thinned wall part is apt to suffer from pin holes. Accordingly,thinned wall parts of all battery vessels must be subject to a pin holetest for detecting the presence of pin holes.

In this manner, with the above-mentioned method, it is extremelydifficult to provide the thinned wall part which has a uniform thicknessso that especially on the condition that the safety valves are to beoperated to release pressure at a low pressure of not more than 30kgf/cm², a reliable reproductivity of the pressure releasing operationcannot be achieved.

To resolve the drawbacks of the above-mentioned methods, Japaneselaid-open publication HEI 5-314959 discloses a method in which a matalplate having a perforated opening and a thin metal plate adhered witheach other to produce a thinned wall part having a uniform thickness andsuch a method provides a valve operating pressure which is not more than30 kgf/cm² and has a reliable reproductivity on a pressure releasingoperation.

In this method, however, since the perforated metal plate and thethinned metal plate are heated in a vacuum furnace and heat-sealed witheach other under pressure, the materials for these metal plates mustmeet a condition that they can be heat-sealed under pressure. Namely,the materials for these metal plates are restricted to same metals ormetals having similar physical properties such as a melting point. InJapanese laid-open publication HEI 5-314959, stainless steel, iron,nickel and the like are proposed as preferable materials for these metalplates.

Furthermore, to heat seal these metal plates under pressure to obtain auniform adhering strength, an oxide film formed on the surface of thesemetal plates must be removed by buffing or the like and then the metalplates must be heated at a high temperature of approximately 1000° C. sothat the method necessitates a sophistiated operation and facilities.Furthermore, these thin metal plates are usually produced by a coldrolling so that they are subjected to hardening by working. Since theabove-mentioned metal plates which are hardened by working are annealedat a high temperature during the heat sealing under pressure, themechanical strength of these metal plates differs before and after theheat sealing operation. Accordingly, the properties of the materialsbefore heat sealing, the heating temperature and the heating time haveto be strictly controlled to make the mechanical strength (the limitstrength which causes a rupture when the inner pressure is elevated) ofthe metal plates constant after heat sealing.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a cladmaterial which is preferably used for producing safety valves whichrupture precisely at a predetermined pressure in a low pressure rangeand which can be manufactured readily.

The clad material according to the present invention is a laminatecomprising a metal substrate which is provided with a multiplicity ofperforated openings and a metal foil which is stacked on the metalsubstrate and laminated thereto so as to close the perforated openings.At least one surface of the metal substrate having a multiplicity ofperforated openings and the mating surface of the metal foil aresubjected to a dry etching and the etched surfaces face each other asthe contacting surfaces of the resultant laminate. In the method aplurality of perforated openings are formed in a metal plate so as toproduce the metal substrate and one surface of the metal substrate issubjected to a dry etching and the metal foil is stacked on the etchedsurface of the metal substrate. In the clad material according to thepresent invention, it is preferable that the metal substrate or themetal foil is provided with a nickel plating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a clad material according tothe present invention.

FIG. 2 is a schematic perspective view showing the manner of producingthe clad material according to the present invention.

FIG. 3 is a schematic perspective view showing the apparatus forproducing the clad material according to the present invention.

FIG. 4 is a schematic view of a safety valve chip produced from the cladmaterial according to the present invention.

FIG. 5 is a schematic view of a lid of a vessel on which the safetyvalve chip is mounted.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The clad material according to the present invention is hereinafterexplained in detail in conjunction with attached drawings.

In FIG. 1, a clad material 19 according to the present invention has alaminar sheet-like construction and is made of a metal substrate 20A anda metal foil 20B which is laminated on the metal substrate 20A. Themetal substrate 20A is provided with a multiplicity of perforatedopenings C. A plurality of safety valve chips D can be readily producedfrom the clad material 19 as described hereinafter.

The safety valve chips D shown in FIG. 4 which are produced from theclad material 19 should be operated at a low pressure of not more than30 kgf/cm², or preferably, of not more than 20 kgf/cm². To achieve thisobjective, the metal foil 20B which can be employed for the presentinvention should have a thickness of 5 to 50 μm corresponding to thekind of metal of the metal foil 20B. In the case that the thickness ofthe metal foil 20B is less than 5 μm, if the safety valve chip D ismounted on the battery as the safety valve, the metal foil 20B readilyruptures when it is dropped on a working table or the like. In the casethat the thickness of the metal foil 20B exceeds 50 μm, even when themetal foil 20B is made of a metal having a low rupture strength, if thesafety valve chip D is mounted on the battery as the safety valve, themetal foil 20B does not rupture at a pressure below 30 kgf/cm² andruptures when a high pressure far exceeding 30 kgf/cm² is applied to themetal foil 20B. In such a case, as the vessel itself ruptures when theinner pressure thereof is elevated, broken pieces of the vessel arescattered around and the content in the vessel is also spilled outsidethus causing a damage on a human body. Furthermore, the use of suchsafety valve chips D having thick metal foil 20B is not favorable interms of the manufacturing cost of the batteries.

In the case that the metal foil 20B is used as the safety valve chip Dof the battery, the kinds of metal foil 20B should preferably be steelfoil, stainles steel foil, copper foil, aluminum foil, nickel foil andnickel-iron alloy foil since the metal foil 20B is required to have afavorable corrosion resistance against alkaline aqueous solution ofelectrolyte.

In the case that the metal foil 20B is used for usages other thanbatteries, any kinds of metal foil B can be used on the condition thatthe metal foil 20B shows a stability against a content filled in avessel, is not corroded and does not gererate a considerable amount of areaction gas. Namely,the metal foil 20B can be made of zinc, lead,copper alloys such brass, bronze, phosphor bronze, gun metal or monelmetal, and aluminum alloy such as duralmin besides the materials asmentioned previously.

Although the metal foil 20B can be produced in any known methods, themetal foil 20B is generally produced by thinning a strip by a coldrolling or by further annealing the thus cold rolled strip.

Although the thickness of metal sheet used for producing metal substrateA is not specifically limited, it should be 0.03 to 0.50 mm usually andpreferably 0.05 to 0.10 mm in view of the strength of the metalsubstrate 20A , an economy of production and for facilitating thewelding or calking of the safety valve chip D to the vessel.

In the safety valve chip D which is made of two metal pieces, namely,the metal foil 20B and the metal substrate 20A , if the metal substrate20A directly comes into contact with alkaline aqueous solution ofelectrolyte, the kinds of metal substrate 20A should preferably be steelplate, stainless steel plate, copper plate, nickel plate and nickel-ironalloy plate since the metal substrate 20A must have a favorablecorrosion resistance against alkaline aqueous solution of electrolyte.

In case that the metal substrate 20A does not directly come into contactwith alkaline aqueous solution, since the metal substrate 20A does nothave to have a favorable resistacnce against alkaline aqueous solution,any metal plate can be used on the condition that the metal plate isstable against a content filled in a vessel, the performance of thebattery is not deteriorated, and a reaction gas is not generated in aconsiderable amount.

The object of the present invention can be achieved even when the kindof metal foil 20B is different from the kind of the metal substrates20A.

Furthermore, although the above-mentioned metal substrate 20A can beproduced by any methods, generally, the metal plate which is thinned bythe cold rolling is directly used as the metal substrate 20A or themetal plate which is produced by further annealing the thinned metalplate after the cold rolling.

The metal substrate 20A is provided with at least one perforated openingC. The size and shape of the perforated opening C differ correspondingto the size and shape of the vessel on which the safety valve chip D ismounted. Accordingly, there is no restriction on the size and shape ofthe perforated opening C. In general, the perforated opening C shouldpreferably be of a circular shape having a diameter of 1 to 10 mm. Theperforated opening C can be of an elliptical shape having a longitudinalaxis length of 1 to 10 mm or of a polygonal shape having a diagonallength which corresponds to the diameter of the above-mentioned circularshape.

The shape of the perforated opening C can be defined by a section of aline such as a straight or curved slit having a desired width.

The shape of the perforated opening C can be defined by a geometricalpattern which is a combination of several kinds of above-mentionedfigures.

These perforated openings C are formed in the metal substrate 20A in adesired shape by a punching press, wherein the metal substrate 20A isproduced by thinning the plates by cold rolling as described previously.These perforated openings C are preferably arranged in a geometricalmanner such as a lattice-like manner or a zigzaging manner. The pitch orinterval between the perforated openings C is determined in a desiredmanner in view of the size of the safety valve chip D. Although themanner of forming such perforated openings C is not restrictedspecifically, the perforated openings C can be formed in conventionalmanners such as punching out the metal substrate 20A with a punchingpress or an etching method.

Furthermore, the clad material may be produced by adhering the metalfoils 20B on both sides of the metal substrate 20A. In this case, evenwhen one metal foil 20B adhered on one surface of the metal substrate20A is broken, so long as the other metal foil 20B adhered to the othersurface of the metal substrate 20A is not broken, the normal function ofthe safety valve can be assured.

The safety valve chip D is generally mounted on the vessel of thebattery by welding in such a manner that the safety valve chip D closesan opening which is formed in a part of the vessel of the battery. Forexample, as shown in FIG. 5, an opening F formed in a lid E of thevessel of the battery is closed by the safety valve chip D.

The perforated opening C is formed in the metal plate to produce themetal substrate 20A and the metal foil 20B is adhered to the metalsubstrate 20A to produce the safety valve chip D and such a safety valvechip D can be directly molded into a lid of the vessel of a battery.

The metal foil 20B and the metal substrate 20A provided with perforatedopenings C are subjected to a pressure welding in a vacuum, for example,by a method disclosed in Japanese laid-open patent publication HEI1-224184.

In FIG. 2 and FIG. 3, an apparatus for producing the clad material 19 bypressure welding a metal foil 20B and a metal substrate 20A in a vacuumis shown in a partial cross section. As shown in these drawings, themetal substrate 20A and the metal foil 20B which are respectivelyreleased from uncoilers 3A, 3B are wound around a pair of electroderolls 6A, 6B which have portions thereof protruding toward an etchingchamber 22 and then they are subjected to a sputtering treatment so asto be activated. Subsequently, the metal substrate 20A and the metalfoil 20B are subjected to a cold rolling by a rolling unit 2 mounted inthe vacuum chamber 1 thus producing the clad material 19 and then theclad material 19 is wound around a coiler 5. The rolling unit 2 isprovided with a rolling reduction device 18 for descending the roll. Thevacuum level in the vacuum chamber 1 is held in a range of 10⁻³ to 10⁻⁶Torr by a large-sized vacuum pump (air exhaust pump) 9.

In the production of the clad material 19, a magnetron sputtering methodis employed for activating the metal foil 20B and the metal substrate20A and a high frequency power source having a frequency range of 1 to50 MHz is employed as a power source for sputtering. In the case thatthe frequency is less than 1 MHz, it is difficult for the high frequencypower source to assure a stable glow discharge so that a continuousetching is not achieved, while in the case that the frequency is morethan 50 MHz, the high frequency power source apts to oscillate so thatthe power supply system becomes unpreferably complicated.

For starting the etching operation, preliminarily, the vacuum level inthe etching chamber 22 has to be held at a pressure not more than 1×10⁻⁴Torr and argon gas is charged into the etching chamber 22 so as toproduce an argon gas atmosphere with a vacuum level of 10⁻¹ to 10⁻⁴Torr. Then, a high frequency current is supplied between the etchingchamber 22 and the vacuum chamber 1, plasma is generated and the surfaceof the metal foil 20B and the surface of the metal substrate 20A areboth subjected to etching.

In the case that the presssure of argon gas is below 1×10⁻⁴ Torr, it isdifficult to assure the stable glow discharge and a high ion flow is notobtained so that a high speed etching becomes difficult. On the otherhand, in the case that the pressure of argon gas exceeds 1×10⁻¹ Torr,the average free path of the sputtered atoms becomes short so that thefreqeuncy that the sputtered atoms are shot again to the target isincreased. Namely, oxygens which are separated from the oxide formed onthe surfaces of the metal foil and the metal substrate by etching areagain shot to the target so that the efficiency of surface activatingtreatment is deteriorated. Accordingly, the pressure of argon gasatmosphere in the etching chamber 22 should be held in a range of 10⁻¹to 10⁻⁴ Torr.

With the use the magnetron sputtering method in the production of cladmaterial 19 of the present invention, an etching speed of more than 1000angstrom/min can be obtained so that even when a stable and thick oxidefilm is formed on the aluminum and titan, such an oxide film can becompletely removed in a few minutes. The oxide film formed on thesurface of copper, steel, stainless steel and amorphous metal canexhibit a clean surface by etching for a few seconds.

Although the lowering of vacuum level in the vacuum chamber 1 leads tothe corresponding lowering of the welding strength of the metal foil 20Bto the metal substrate 20A, an allowable lower limit of the vacuum levelin the vacuum chamber 1 should be 1×10⁻¹ Torr in view of industrialeconomy, while the upper limit should be 1×10⁻³ Torr since this level ofvacuum still assures a sufficient welding strength.

Furtheremore, in the production of the clad material 19, it isunnecessary to heat the metal foil 20B and the metal substrate 20Aduring a cold rolling. Namely, in the cold rolling, there is no problemeven if the temperature T of these metals 20A, 20B at the time ofgripping them between rolls is held at a room temperature. However, ifit becomes necessary to heat the metal foil 20B and the metal substrate20A during the cold rolling in view of decreasing the difference of thethermal expansion rates of these metals 20A, 20B caused by a heatgenerated at the time of rolling as well as accompanying deformation ofthese metals 20A,20B after being cooled, the upper limit of heatingshould preferably be not more than 300° C. so as to prevent theoccurrence of recrystallizing annealing, an alloy layer or carbide whichdeteriorate the welding strength between these metals 20A and 20B.

The rolling reduction rate at the time of cold rolling the metal foil20B and the metal substrate 20A should preferably be 0.1 to 30% .Namely, cold rolling shoud be carried out with the rolling reductionrate which falls in a range expressed as follows. ##EQU1##

The lower limit of the rolling reduction rate is determined by followingfactors. Namely, although the surface of the plate appears flat at aglance, there are many fine or minute irregularities or indentations ina microscopic level and metals come into cotact with each other with anextremely insufficient contact area if pressure is not applied to themand under a conventional cold rolling welding method, a strong weldingcannot be obtained even if the surfaces of these metals are sufficientlyactivated. Accordingly, in the conventional cold rolling welding method,the oxide film on the surfaces of these metals are subjected to aplastic flow by a cold rolling with a high rolling reduction rate sothat the surfaces of the metals are partially activated and the contactarea is increased and then the metals are welded each other. In such amethod, the surfaces of the metals are not necessarily flat. Namely, themetal substrate is preliminarily finished at a reasonable roughness andthen is subjected to the cold rolling with a high rolling reduction rateto make the surfaces flat and smooth.

On the other hand, in purifying the surfaces of the metal foil 20B andthe metal substrate 20A by the method for producing clad materialaccording to the present invention, no new irregularities orindentations are formed on the surfaces of the metal foil 20B and themetal substrate 20A. Then, the metal foil 20B and the metal substrate20A can be pressure welded while keeping a surface flatness at the timeof finish rolling carried out before pressure welding. Accordingly, evenwith a small pressure, a sufficient contact area is obtained and ametallic bonding steadily takes place on the contact portions so that astrong adhering strength is obtained even with the small rollingreduction rate.

Considering a case that the plate is subjected to a cold rolling and afinishing rolling or to a refining rolling in one rolling step, theupper limit of the rolling reduction rate is determined to be 30% . Itis not desirable that the rolling reduction rate exceeds 30% since suchrolling rate gives rise to an extremely high work hardness. For pressurewelding the metal foil 20B and the metal substrate 20A in a coldrolling, in place of rolling roll, a pressurizing mechanism such as apress which is provided with a flat block at one side thereof or flatblocks at both sides thereof can be used.

The present invention is further explained in conjunction with followingpreferred examples.

EXAMPLE 1

A multiplicity of circular perforated openings having a diameter of 3 mmwere formed on the cold rolled steel plate (metal plate) having athickness of 90 μm in a lattice pattern by means of a punching press,wherein a pitch between openings was determined to be 10 mm. A nickelplating having a thickness of 2 μm was applied to both surfaces of theperforated steel plate by means of a Watt bath to produce a metalsubstrate.

This metal substrate and an aluminum foil having a thickness of 30 μmwere inserted into a vacuum chamber of an argon gas atmosphere having avacuum level of 5×10⁻³ Torr so as to provide an etching of approximately100 angstrom on one surface of the metal substrate and an etching ofapproximately 2000 angstrom on the corresponding one surface of thealuminum foil by the magnetron sputtering method. Subsequently, themetal substrate and the aluminum foil were laminated in a manner thatthe etched surfaces of them are contacting each other and pressurewelded by a cold rolling at a temperature of 120° C. and with a rollingreduction rate of 3% to produce a clad material. A multiplicity ofsafety valve chips for battery use were punched from the clad material,wherein each safety valve chip was of a rectangular shape having alongitudinal length of 10.5 mm and a lateral length of 7.5 mm and wasprovided with one circular opening at the center thereof.

Each safety valve chip for battery use was welded to a steel-plate-madepressure vessel in such a manner that the safety valve chip hermeticallyclosed a perforated opening formed in the pressure vessel, wherein thepressure vessel was provided with one end through which a compressed airis supplied to the pressure vessel so as to pressurize the inside of thepressure vessel.

Then, a edge part of the steel-plate-made pressure vessel was connectedwith an air compressor by way of a pressure gauge and the inside of thepressure vessel was pressurized. When the inner pressure of the pressurevessel reached 14 kgf/cm², the aluminum foil of the safety valve chipfor battery use ruptured.

Thereafter, several safety valve chips for battery use were hermeticallywelded to the steel-plate-made pressure vessels and the inner pressureof the pressure vessels was increased. The aluminum foils of all sefetyvalve chips for battery use ruptured at pressures which fall in a stablepressure range of 12 to 18 kgf/cm².

EXAMPLE 2

A multiplicity of circular perforated openings having a diameter of 3 mmwere formed in a cold-rolled stainless steel plate having a thickness of60 μm in a lattice pattern by means of a punching press, wherein a pitchbetween openings was determined to be 10.5 mm. This perforatedcold-rolled stainless steel plate and a nickel foil having a thicknessof 10 μm were inserted into a vacuum chamber of an argon gas atmospherehaving a vacuum level of 1×10⁻² Torr so as to provide an etching ofapproximately 500 angstrom on one surface of the cold-rolled perforatedstainless steel plate and an etching of approximately 500 angstrom onthe corresponding one surface of the nickel foil by the magnetronsputtering method. Subsequently, the etched surfaces of the thecold-rolled and perforated stainless steel plate and the nickel foilwere laminated and both plate and foil were pressure welded by a coldrolling at a room temperature and with a rolling reduction rate of 0.5%to produce a clad material. Seven safety valve chips for battery usewere punched from the clad material, wherein each safety valve chip wasof a rectangular shape having a longitudinal length of 10.5 mm and alateral length of 7.5 mm and was provided with one circular opening atthe center thereof.

These safety valve chips for battery use were hermetically welded to asteel-plate-made pressure vessels in the same manner as that of theexample 1. and as a result, the nickel foils of seven safety valve chipsfor battery use ruptured at pressures which fall in a stable pressurerange of 13 to 17 kgf/cm².

EXAMPLE 3

A multiplicity of circular perforated openings having a diameter of 3 mmwere formed on a cold rolled steel plate (metal plate) having athickness of 90 μm in a zigzaging pattern by means of a punching press,wherein a pitch between openings was determined to be 10.5 mm. A nickelplating having a thickness of 2 μm was applied to both surfaces of thecold rolled steel plate in the same manner as that of the example 1.

This nickel-plated and perforated steel plate and a copper foil having athickness of 10 μm were inserted into a vacuum chamber of an argon gasatmosphere having a vacuum level of 2×10⁻¹ Torr so as to provide anetching of approximately 500 angstrom on one surface of the nickelplated steel plate and an etching of approximately 500 angstrom on thecorresponding one surface of the copper foil by the magnetron sputteringmethod. Subsequently, the etched surfaces of the nickel plated steelplate and the copper foil were laminated and pressure welded by a coldrolling at a room temperature and with a rolling reduction rate of 0.3%to produce a clad material. Seven safety valve chips for battery usewere punched from the clad material, wherein each valve element was of acircular shape having a diameter of 10.5 mm and was provided with onecircular opening at the center thereof.

These safety valve chips for battery use were hermetically welded to asteel-plate-made pressure vessels in the same manner as that of theexample 1. Then, the inside of pressure vessel was pressurized in thesame manner as that of the example 1, as a result the copper foils ofthese safety valve chips ruptured in a stable pressure range of 10 to 15kgf/cm².

(control--heating pressure welding under high temperature)

In a nickel-plated steel plate which was produced in the same manner asthat of the example 3, a multiplicity of circular openings were formedin a zigzaging pattern in the same manner as that of the example 3. Thisnickel-plated steel plate and a copper foil similar to that of the theexample 3 were laminated and heat sealed under pressure in a vacuumfurnace at a temperature of 1000° C. , seven safety valve chips eachhaving a circular dent at the center thereof were produced from thislaminated plate. After hermetically welding these safety valve chips tothe pressure vessel, the inside of the steel-made pressure vessel waspressurized, and as a result the nickel foils of these safety valvechips ruptured in a wide pressure range of 4 to 12 kgf/cm².

As has been described heretofore, the clad material according to thepresent invention can be effectively used for producing safety valvechips which rupture accurately at low pressures which fall in a stablepressure range on a mass production basis.

What is claimed is:
 1. Clad material comprising a metal substrateprovided with a multiplicity of perforated openings therein and a metalfoil laminated on said metal substrate so as to close said perforatedopenings.
 2. Clad material according to claim 1, wherein at least onesurface of said metal substrate and corresponding one surface of saidmetal foil are respectively subjected to a dry etching to provide etchedsurfaces and said metal substrate and said metal foil are laminated in amanner that said etched surfaces face each other.
 3. Clad materialaccording to claim 1, wherein one surface of said metal substrate issubjected to a dry etching and said metal substrate and said metal foilare laminated in a manner that said etched surface faces said metalfoil.
 4. Clad material according to claim 1, wherein said metalsubstrate or said metal foil is provided with a nickel plating.
 5. Cladmaterial according to claim 2, wherein said metal substrate or saidmetal foil is provided with a nickel plating.
 6. Clad material accordingto claim 3, wherein said metal substrate or said metal foil is providedwith a nickel plating.